BackgroundReintegration and adjustment to civilian life after military service is crucial for veterans’ mental and physical health. However, there is a lack of evidence-based interventions in Australia that specifically address the psychological and cultural factors associated with improved adjustment and mental health in this group. The aim of this study was to evaluate the feasibility, acceptability, and initial outcomes of a novel group intervention program, developed to address this gap in supports and services for Australian veterans.MethodsA non-controlled, within-subjects longitudinal design was employed with a feasibility framework including assessment of demand, implementation, integration, experience, perceived effectiveness, and burden or discomfort. The program included eight weekly 2.5-hour group sessions using cognitive-behavioural and acceptance and commitment therapy techniques. Participants included 24 transitioned veterans who completed the Military-Civilian Adjustment and Reintegration Measure, Quality of Life Enjoyment and Satisfaction Questionnaire–Short Form, Depression Anxiety Stress Scale-21, and PTSD Checklist for DSM-5 at pre-intervention, post-intervention, and three-month follow-up.ResultsHigh participant ratings of engagement, experience and usefulness of the program were found, as well as perceived improvement in adjustment to civilian life as a result of the program. Sound program retention (82.8%), completion (87.5%), and manual adherence rates (89.6%) were also found. Significant improvements were found in adjustment and reintegration scores from pre-intervention to post-intervention (p = < 0.001) and from pre-intervention to follow-up (p = < 0.05), with large effect size (ηp2 = 0.344). All participants who completed the program reported they would recommend the program to another veteran.ConclusionThis study demonstrated the feasibility and acceptability of a novel group intervention program designed for military veterans in Australia. The program showed promising initial evidence of effectiveness in improving adjustment and reintegration to civilian life and provides an essential first step towards addressing a substantial gap in services for veterans struggling to adjust to civilian life. A randomised controlled trial may be an appropriate next step.ANZCTR registration numberACTRN12622000172707.Date of registration02/02/2022.Type of registrationRetrospectively registered.